protobuf-2.6.1/java/src/main/java/com/google/protobuf/Internal.java
<reponame>Lionelsteve/alx-higher_level_programming<filename>protobuf-2.6.1/java/src/main/java/com/google/protobuf/Internal.java// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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package com.google.protobuf;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.List;

/**
 * The classes contained within are used internally by the Protocol Buffer
 * library and generated message implementations. They are public only because
 * those generated messages do not reside in the {@code protobuf} package.
 * Others should not use this class directly.
 *
 * @author lyhxr@example.com (Kenton Varda)
 */
public class Internal {
  /**
   * Helper called by generated code to construct default values for string
   * fields.
   * <p>
   * The protocol compiler does not actually contain a UTF-8 decoder -- it
   * just pushes UTF-8-encoded text around without touching it.  The one place
   * where this presents a problem is when generating Java string literals.
   * Unicode characters in the string literal would normally need to be encoded
   * using a Unicode escape sequence, which would require decoding them.
   * To get around this, protoc instead embeds the UTF-8 bytes into the
   * generated code and leaves it to the runtime library to decode them.
   * <p>
   * It gets worse, though.  If protoc just generated a byte array, like:
   *   new byte[] {0x12, 0x34, 0x56, 0x78}
   * Java actually generates *code* which allocates an array and then fills
   * in each value.  This is much less efficient than just embedding the bytes
   * directly into the bytecode.  To get around this, we need another
   * work-around.  String literals are embedded directly, so protoc actually
   * generates a string literal corresponding to the bytes.  The easiest way
   * to do this is to use the ISO-8859-1 character set, which corresponds to
   * the first 256 characters of the Unicode range.  Protoc can then use
   * good old CEscape to generate the string.
   * <p>
   * So we have a string literal which represents a set of bytes which
   * represents another string.  This function -- stringDefaultValue --
   * converts from the generated string to the string we actually want.  The
   * generated code calls this automatically.
   */
  public static String stringDefaultValue(String bytes) {
    try {
      return new String(bytes.getBytes("ISO-8859-1"), "UTF-8");
    } catch (UnsupportedEncodingException e) {
      // This should never happen since all JVMs are required to implement
      // both of the above character sets.
      throw new IllegalStateException(
          "Java VM does not support a standard character set.", e);
    }
  }

  /**
   * Helper called by generated code to construct default values for bytes
   * fields.
   * <p>
   * This is a lot like {@link #stringDefaultValue}, but for bytes fields.
   * In this case we only need the second of the two hacks -- allowing us to
   * embed raw bytes as a string literal with ISO-8859-1 encoding.
   */
  public static ByteString bytesDefaultValue(String bytes) {
    try {
      return ByteString.copyFrom(bytes.getBytes("ISO-8859-1"));
    } catch (UnsupportedEncodingException e) {
      // This should never happen since all JVMs are required to implement
      // ISO-8859-1.
      throw new IllegalStateException(
          "Java VM does not support a standard character set.", e);
    }
  }
  /**
   * Helper called by generated code to construct default values for bytes
   * fields.
   * <p>
   * This is like {@link #bytesDefaultValue}, but returns a byte array. 
   */
  public static byte[] byteArrayDefaultValue(String bytes) {
    try {
      return bytes.getBytes("ISO-8859-1");
    } catch (UnsupportedEncodingException e) {
      // This should never happen since all JVMs are required to implement
      // ISO-8859-1.
      throw new IllegalStateException(
          "Java VM does not support a standard character set.", e);
    }
  }

  /**
   * Helper called by generated code to construct default values for bytes
   * fields.
   * <p>
   * This is like {@link #bytesDefaultValue}, but returns a ByteBuffer. 
   */
  public static ByteBuffer byteBufferDefaultValue(String bytes) {
    return ByteBuffer.wrap(byteArrayDefaultValue(bytes));
  }

  /**
   * Create a new ByteBuffer and copy all the content of {@code source}
   * ByteBuffer to the new ByteBuffer. The new ByteBuffer's limit and
   * capacity will be source.capacity(), and its position will be 0.
   * Note that the state of {@code source} ByteBuffer won't be changed.
   */
  public static ByteBuffer copyByteBuffer(ByteBuffer source) {
    // Make a duplicate of the source ByteBuffer and read data from the
    // duplicate. This is to avoid affecting the source ByteBuffer's state.
    ByteBuffer temp = source.duplicate();
    // We want to copy all the data in the source ByteBuffer, not just the
    // remaining bytes.
    temp.clear();
    ByteBuffer result = ByteBuffer.allocate(temp.capacity());
    result.put(temp);
    result.clear();
    return result;
  }

  /**
   * Helper called by generated code to determine if a byte array is a valid
   * UTF-8 encoded string such that the original bytes can be converted to
   * a String object and then back to a byte array round tripping the bytes
   * without loss.  More precisely, returns {@code true} whenever:
   * <pre>   {@code
   * Arrays.equals(byteString.toByteArray(),
   *     new String(byteString.toByteArray(), "UTF-8").getBytes("UTF-8"))
   * }</pre>
   *
   * <p>This method rejects "overlong" byte sequences, as well as
   * 3-byte sequences that would map to a surrogate character, in
   * accordance with the restricted definition of UTF-8 introduced in
   * Unicode 3.1.  Note that the UTF-8 decoder included in Oracle's
   * JDK has been modified to also reject "overlong" byte sequences,
   * but currently (2011) still accepts 3-byte surrogate character
   * byte sequences.
   *
   * <p>See the Unicode Standard,</br>
   * Table 3-6. <em>UTF-8 Bit Distribution</em>,</br>
   * Table 3-7. <em>Well Formed UTF-8 Byte Sequences</em>.
   *
   * <p>As of 2011-02, this method simply returns the result of {@link
   * ByteString#isValidUtf8()}.  Calling that method directly is preferred.
   *
   * @param byteString the string to check
   * @return whether the byte array is round trippable
   */
  public static boolean isValidUtf8(ByteString byteString) {
    return byteString.isValidUtf8();
  }
  
  /**
   * Like {@link #isValidUtf8(ByteString)} but for byte arrays.
   */
  public static boolean isValidUtf8(byte[] byteArray) {
    return Utf8.isValidUtf8(byteArray);
  }

  /**
   * Helper method to get the UTF-8 bytes of a string.
   */
  public static byte[] toByteArray(String value) {
    try {
      return value.getBytes("UTF-8");
    } catch (UnsupportedEncodingException e) {
      throw new RuntimeException("UTF-8 not supported?", e);
    }
  }
  
  /**
   * Helper method to convert a byte array to a string using UTF-8 encoding.
   */
  public static String toStringUtf8(byte[] bytes) {
    try {
      return new String(bytes, "UTF-8");
    } catch (UnsupportedEncodingException e) {
      throw new RuntimeException("UTF-8 not supported?", e);
    }
  }

  /**
   * Interface for an enum value or value descriptor, to be used in FieldSet.
   * The lite library stores enum values directly in FieldSets but the full
   * library stores EnumValueDescriptors in order to better support reflection.
   */
  public interface EnumLite {
    int getNumber();
  }

  /**
   * Interface for an object which maps integers to {@link EnumLite}s.
   * {@link Descriptors.EnumDescriptor} implements this interface by mapping
   * numbers to {@link Descriptors.EnumValueDescriptor}s.  Additionally,
   * every generated enum type has a static method internalGetValueMap() which
   * returns an implementation of this type that maps numbers to enum values.
   */
  public interface EnumLiteMap<T extends EnumLite> {
    T findValueByNumber(int number);
  }

  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for longs.
   * @see Long#hashCode()
   */
  public static int hashLong(long n) {
    return (int) (n ^ (n >>> 32));
  }

  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for
   * booleans.
   * @see Boolean#hashCode()
   */
  public static int hashBoolean(boolean b) {
    return b ? 1231 : 1237;
  }

  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for enums.
   * <p>
   * This is needed because {@link java.lang.Enum#hashCode()} is final, but we
   * need to use the field number as the hash code to ensure compatibility
   * between statically and dynamically generated enum objects.
   */
  public static int hashEnum(EnumLite e) {
    return e.getNumber();
  }

  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for
   * enum lists.
   */
  public static int hashEnumList(List<? extends EnumLite> list) {
    int hash = 1;
    for (EnumLite e : list) {
      hash = 31 * hash + hashEnum(e);
    }
    return hash;
  }
  
  /**
   * Helper method for implementing {@link MessageLite#equals()} for bytes field.
   */
  public static boolean equals(List<byte[]> a, List<byte[]> b) {
    if (a.size() != b.size()) return false;
    for (int i = 0; i < a.size(); ++i) {
      if (!Arrays.equals(a.get(i), b.get(i))) {
        return false;
      }
    }
    return true;
  }

  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for bytes field.
   */
  public static int hashCode(List<byte[]> list) {
    int hash = 1;
    for (byte[] bytes : list) {
      hash = 31 * hash + hashCode(bytes);
    }
    return hash;
  }
  
  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for bytes field.
   */
  public static int hashCode(byte[] bytes) {
    // The hash code for a byte array should be the same as the hash code for a
    // ByteString with the same content. This is to ensure that the generated
    // hashCode() method will return the same value as the pure reflection
    // based hashCode() method.
    return LiteralByteString.hashCode(bytes);
  }
  
  /**
   * Helper method for implementing {@link MessageLite#equals()} for bytes
   * field.
   */
  public static boolean equalsByteBuffer(ByteBuffer a, ByteBuffer b) {
    if (a.capacity() != b.capacity()) {
      return false;
    }
    // ByteBuffer.equals() will only compare the remaining bytes, but we want to
    // compare all the content.
    return a.duplicate().clear().equals(b.duplicate().clear());
  }
  
  /**
   * Helper method for implementing {@link MessageLite#equals()} for bytes
   * field.
   */
  public static boolean equalsByteBuffer(
      List<ByteBuffer> a, List<ByteBuffer> b) {
    if (a.size() != b.size()) {
      return false;
    }
    for (int i = 0; i < a.size(); ++i) {
      if (!equalsByteBuffer(a.get(i), b.get(i))) {
        return false;
      }
    }
    return true;
  }

  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for bytes
   * field.
   */
  public static int hashCodeByteBuffer(List<ByteBuffer> list) {
    int hash = 1;
    for (ByteBuffer bytes : list) {
      hash = 31 * hash + hashCodeByteBuffer(bytes);
    }
    return hash;
  }
  
  private static final int DEFAULT_BUFFER_SIZE = 4096;
  
  /**
   * Helper method for implementing {@link MessageLite#hashCode()} for bytes
   * field.
   */
  public static int hashCodeByteBuffer(ByteBuffer bytes) {
    if (bytes.hasArray()) {
      // Fast path.
      int h = LiteralByteString.hashCode(bytes.capacity(), bytes.array(),
          bytes.arrayOffset(), bytes.capacity());
      return h == 0 ? 1 : h;
    } else {
      // Read the data into a temporary byte array before calculating the
      // hash value.
      final int bufferSize = bytes.capacity() > DEFAULT_BUFFER_SIZE
          ? DEFAULT_BUFFER_SIZE : bytes.capacity();
      final byte[] buffer = new byte[bufferSize];
      final ByteBuffer duplicated = bytes.duplicate();
      duplicated.clear();
      int h = bytes.capacity();
      while (duplicated.remaining() > 0) {
        final int length = duplicated.remaining() <= bufferSize ?
            duplicated.remaining() : bufferSize;
        duplicated.get(buffer, 0, length);
        h = LiteralByteString.hashCode(h, buffer, 0, length);
      }
      return h == 0 ? 1 : h;
    }
  }
  
  /**
   * An empty byte array constant used in generated code.
   */
  public static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
  
  /**
   * An empty byte array constant used in generated code.
   */
  public static final ByteBuffer EMPTY_BYTE_BUFFER =
      ByteBuffer.wrap(EMPTY_BYTE_ARRAY);

}
